Overhauling Hydraulic Rams

[Phill]

I have two identical sets of Hydraulic rams. Whilst all operate normally they don't maintain the negative hold down pressure for any length of time. I have tried swapping rams but still lose the negative hold down pressure so suspect all need an overhaul to restore their performance.

Each ram has 4 different O rings, after carefully measuring each ring along with the bores of the ram and checking available sizes of O rings I have arrived at the following sizes for each ring

14mm ID x 19mm OD
15.6mm ID x 19.16 OD
12mm ID x 17mm OD
6.07mm ID x 9.63mm OD

However, I suspect the old rings will be slightly worn so I am worried that the new rings (which are the same size) would not restore performance. How do I go about determining what size each O ring neds to be? There are no marking on the rams to determine the original manufacturer though I suspect these are original Elam era rams supplied by the factory along with the Smiths pump.

Any advice gratefully received?

[steve]

[...] I have tried swapping rams but still lose the negative hold down pressure so suspect all need an overhaul to restore their performance.

Hmmm... how do you know that it is the rams and not the valves in that dodgy pump I sold you? ;-)

You have swapped rams around, which didn't solve the problem.
The pump is the common denominator here.

[Phill]

I don't think you would sell me a dodgy pump would you Steve?

Actually, the first thing I changed was the pump which made no difference. Later I noticed one of my original rams was weeping oil at the top seal so I elected to fit one of the Rams I got from you. This didn't help (In fact it made it worse) so I have concluded that the rams are most likely at fault (either that or I have two faulty pumps). Laurens advice some time ago was that the Rams were more likely to be at fault than the Smiths pumps (which have a reputation for being highly robust). I have already stripped down the two spare rams (all four are identical) and while they are stripped down I have introduced copper sleeves to prevent the rams opening the roof over centre as suggested by Dave (Islandman). They are limited to a 19cm maximum extension now.

I have already ordered the new O Rings but still have my concerns over whether or not they are the right size . I don't want to go to all the trouble of fitting the "refurbished" Rams into the car only to find they are fitted with the wrong size of O ring

[Dirk]

I may be wrong but I would question the sizes you are quoting, I would have thought they would have been an imperial size. I would take them to your local hydraulic shop I am sure they can supply rings for pence. That's all they cost me a few years ago and even test the rams phone a few tomorrow.

Dirk

[MartinB]

I took my rams to TVH hydraulics in Didcot and they referbished them and fitted new seals for around £20... (If I remember, it was a few years ago!)
Hope the new O-rings work! `¬)

[Piperphasetwo]

I have already ordered the new O Rings but still have my concerns over whether or not they are the right size . I don't want to go to all the trouble of fitting the "refurbished" Rams into the car only to find they are fitted with the wrong size of O ring

Hi Phill,

Please see the following information

https://www.marcorubber.com/o-ring-g...mic-piston.htm

The application for dynamic O rings is what you need (seals are intended for moving shafts) so the seal location sizes are a slightly different size or shape to a static sealing application.

If you can measure the dimensions of the o ring locations then it hopefully will identify the correct o ring for that position. The linked table is imperial so hopefully it will provide the correct answer..... unless the seals were "special".

Ensure that the bore of the cylinders, piston rod and the O ring grooves are not scored, its not good enough just fitting new seals if there are any axial scores or marks in the bore / shaft / seal location. If there are any marks then polishing or fine honing the cylinder bores, shafts or seal locations is a good idea as long as they were not originally plated.

Regards,

John

[Phill]

Thanks for all the advice guys - I'm more baffled than ever now. The new O rings arrived today so I think I will just give it a go and try changing them over on one Ram first of all to see how it goes

[Phill]

The new seals look identical to the old seals so I went ahead and fitted them and will eventually get around to changing the rams on the car to see if these are any better now


(Old seals Top - New seals Bottom in picture below)
IMG_8647[1].jpg

If nothing else the addition of a copper sleeve as suggested by Dave (Islandman) will make an improvement by preventing the roof from going to far up and over the pivot point

IMG_8648[1].jpg
(Above - Ram components with new O rings fitted ready for re-assembly - Note the addition of the copper sleeve to limit the rams extension)